title: Nasopharyngeal carriage of pneumococci four years after community-wide vaccination with PCV-7 in The Gambia: long-term evaluation of a cluster randomized trial.
abstract: BACKGROUND
  A village-randomized trial of a seven-valent pneumococcal-conjugate-vaccine (PCV-7) conducted in rural Gambia showed a decrease of vaccine-type (VT) and a non-significant increase in non-vaccine-type (NVT) nasopharyngeal carriage of pneumococci two years after vaccination. Here, we report findings four years after vaccination.
  
  
  METHODS
  PCV-7 was given to all children below 30 months of age enrolled in the trial and to those born during its course in all study villages. Villages were randomized (older children and adults) to receive PCV-7 (wholly vaccinated villages) or serogroup-C-meningococcal-conjugate-vaccine (partly vaccinated villages). Cross-sectional surveys (CSS) to collect nasopharyngeal swabs were conducted before and at various intervals after vaccination. Sixteen of these randomized villages (8 wholly vaccinated and 8 partly vaccinated) participated in a CSS conducted four years after vaccination started.
  
  
  RESULTS
  Four years after vaccination, the prevalence of VT pneumococcal carriage was slightly higher in partly than in wholly vaccinated villages [6.4% versus 3.9% (p = 0.120)] compared to 24.4% in the pre-vaccination CSS (p<0.001). Prevalence of NVT four years after vaccination was similar between study groups [32.7% versus 29.8% (p = 0.392), respectively] compared to 51.1% in the pre-vaccination CSS (p<0.001). Four years after vaccination started, lower prevalence of serotype 6A was detected in wholly vaccinated than in partly vaccinated villages (1.6% versus 3.5%, p = 0.093) whilst the prevalence of serotype 19A was similar between groups (2.9% versus 2.5%, p = 0.779). The most prevalent serotype 19A clone was ST 847. The most prevalent serotype 6A clone before vaccination was ST3324 whilst after vaccination ST913 and ST1737 predominated. Fourteen out of 26 STs detected among the serotype 6A isolates were new while no new 19A serotype ST was found.
  
  
  CONCLUSIONS
  The decline in prevalence of VT pneumococci seen shortly after PCV-7 vaccination was sustained four years later with only a small difference between study arms. No significant serotype replacement was detected.
  
  
  BACKGROUND
  ClinicalTrials.gov ISRCTN51695599.
authors.affiliation: Medical Research Council Unit, Banjul, The Gambia.
authors.forename: Anna
authors.initials: A
authors.lastname: Roca
authors.forename: Michel M
authors.initials: MM
authors.lastname: Dione
authors.forename: Abdoulie
authors.initials: A
authors.lastname: Bojang
authors.forename: John
authors.initials: J
authors.lastname: Townend
authors.forename: Uzochukwu
authors.initials: U
authors.lastname: Egere
authors.forename: Ousainou
authors.initials: O
authors.lastname: Darboe
authors.forename: Stephen R C
authors.initials: SR
authors.lastname: Howie
authors.forename: Philip C
authors.initials: PC
authors.lastname: Hill
authors.forename: Richard A
authors.initials: RA
authors.lastname: Adegbola
authors.forename: Brian M
authors.initials: BM
authors.lastname: Greenwood
authors.forename: Martin
authors.initials: M
authors.lastname: Antonio
mesh_terms: D000293:Adolescent; D002648:Child; D002675:Child, Preschool; D016000:Cluster Analysis; D003430:Cross-Sectional Studies; D005260:Female; D005500:Follow-Up Studies; D005714:Gambia; D006801:Humans; D008297:Male; D009305:Nasopharynx / Q000382:microbiology*; D022242:Pneumococcal Vaccines / Q000008:administration & dosage; D013296:Streptococcus pneumoniae / Q000276:immunology / Q000302:isolation & purification*
chemical_list: D022242:Pneumococcal Vaccines